Here's an example that hopefully clears up the usage:

use strict;
use warnings;
use Class::Struct;

struct ( 'Structname', { value1 => '$', value2 => '$' } );

sub myfunction {
    my $mystruct = shift;  # alternatively: my $mystruct = $_[0];
    return $mystruct->value1." ".$mystruct->value2;
}

my $mystruct = new Structname;
$mystruct->value1('foo');
$mystruct->value2(42);
my $value = myfunction($mystruct);

print "$value\n";   # "foo 42"
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(This also works if you put the sub in a separate file that you then require.)